This invention relates to motor assemblies, such as constant torque spring motor assemblies. More particularly, the invention relates to motor assemblies which can be preassembled, e.g., in the form of a cartridge, and rapidly, safely and easily installed for effective use in a desired application.
In many applications where a motor is used to perform one or more functions, the motor itself becomes worn or otherwise requires replacement independently of the other system components. In order to avoid excessive downtime and maintain the desired operation, the defective motor should be replaced as quickly as possible. One approach to this problem has been to package the motor assembly as a cartridge unit, making it a relatively easy matter to remove the old motor and replace it with the cartridge unit.
One application in which a motor assembly cartridge is used is in tank gaging systems. Typically, a tank gaging system involves a spring motor, e.g., a substantially constant torque spring motor, which acts directly to apply a force on a spring hub which, in turn, acts to rotate a drum around which the gage tape is wound.
Motor cartridges, such as the spring motor cartridge sold by Gauging Systems, Inc under the trademark GSI-NC currently in use with tank gaging systems have several drawbacks. Such spring motor cartridges include cases which are made of three separate pieces held together by ten or more fasteners, e.g., screws. The aluminum front and back of these cases are both substantially solid, having only two relatively small holes, and cover both the spring motor and the spring hub. This configuration results in several difficulties. First, the large number of fasteners makes the cartridge itself rather difficult to assemble. Further, by substantially enclosing the entire spring motor and spring hub, the cartridge case allows only very limited access to these components. Thus, the spring can be wound or unwound, e.g., during installation, only by using a specially configured crank which fits through one of the relatively small holes.
An additional and important disadvantage of the currently used spring motor cartridges is the friction which occurs between both the front and back of the cartridge case and the spring hub. This friction detrimentally affects the accuracy of the overall tank gaging system. Clearly a new motor assembly cartridge, e.g., a spring motor cartridge, would be advantageous.